RESUMEN
Okadaic acid (OKA) is a potent inhibitor of protein phosphatases 1/2A (PP2A). Inhibition of PP2A leads to hyperphosphorylation of Tau protein. Hyperphosphorylated Tau protein is present in intraneuronal neurofibrillary tangles a characteristic feature of neuropathology of Alzheimer's disease. Intracerebroventricular (ICV) administration of OKA causes neurotoxicity, which is associated with increased intracellular Ca(2+) level, oxidative stress, and mitochondrial dysfunction in the brain areas. The present study explored Tau phosphorylation in OKA-treated rats in relation to memory function, PP2A activity, intracellular Ca(2+), glycogen synthase kinase-3ß (GSK-3ß) and N-methyl-d-aspartate (NMDA) receptor after 13days of OKA (200ng, ICV) administration in rats, memory was found impaired in the water maze test. OKA-induced memory-impaired rats showed increased mRNA and protein expression of Tau, Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), Calpain and GSK3ß in the hippocampus and cerebral cortex. On the other hand, mRNA expression and activity of PP2A was reduced in these brain areas. OKA treatment also, resulted in decrease in mRNA expression of C and N terminals of Tau. Treatment with NMDA antagonist, MK801 (0.05mg/kg, i.p.) for 13days significantly prevented OKA-induced changes in the expression of PP2A, Tau, GSK3ß, CaMKII and Calpain. Further, daily administration of anticholinergic drug, donepezil (5mg/kg, p.o.), and the NMDA receptor antagonist, memantine (10mg/kg, p.o.) initiated after OKA administration for 13days significantly attenuated OKA-induced variation in Tau, Tau-C terminal, Tau-N terminal CaMKII, Calpain, PP2A and GSK3ß. These results infer that NMDA antagonist MK801 and memantine are effective against OKA-induced neurotoxicity. Therefore, the present study clearly indicates the involvement of NMDA receptor in OKA (ICV)-induced Tau hyperphosphorylation.
Asunto(s)
Encéfalo/efectos de los fármacos , Inhibidores Enzimáticos/farmacología , Ácido Ocadaico/farmacología , Receptores de N-Metil-D-Aspartato/metabolismo , Proteínas tau/metabolismo , Animales , Encéfalo/metabolismo , Calcio/metabolismo , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/metabolismo , Calpaína/metabolismo , Antagonistas Colinérgicos/farmacología , Maleato de Dizocilpina/farmacología , Donepezilo , Antagonistas de Aminoácidos Excitadores/farmacología , Glucógeno Sintasa Quinasa 3/metabolismo , Glucógeno Sintasa Quinasa 3 beta , Indanos/farmacología , Masculino , Aprendizaje por Laberinto/efectos de los fármacos , Memantina/farmacología , Neuronas/efectos de los fármacos , Neuronas/metabolismo , Fosfoproteínas Fosfatasas/antagonistas & inhibidores , Fosforilación/efectos de los fármacos , Piperidinas/farmacología , Ratas , Ratas Sprague-DawleyRESUMEN
The present study was conducted to correlate rotenone-induced neurotoxicity with cellular and molecular modifications in neuronal and neuronal supportive cells in rat brain regions. Rotenone was administered (3, 6 and 12 µg/µl) intranigrally in adult male Sprague-Dawley rats. After the 7th day of rotenone treatment, specific protein markers for neuronal cells - tyrosine hydroxylase (TH), astroglial cells - glial fibrillary acidic protein (GFAP), microglial cells - CD11b/c, and Iba-1 were evaluated by immunoblotting and immunofluorescence in the striatum (STR) and mid brain (MB). Apoptotic cell death was assessed by caspase-3 gene expression. Higher doses of rotenone significantly lowered TH protein levels and elevated Iba-1 levels in MB. All the doses of rotenone significantly increased GFAP and CD11b/c protein in the MB. In STR, rotenone elevated GFAP levels but did not affect TH, CD11b/c and Iba-1 protein levels. Caspase-3 expression was increased significantly by all the doses of rotenone in MB but in STR only by higher doses (6 and 12 µg). It may be suggested that astroglial activation and apoptosis play an important role in rotenone-induced neurotoxicity. MB appeared as more sensitive than STR toward rotenone-induced cell toxicity. The astroglial cells emerged as more susceptible than neuronal and microglial cells to rotenone in STR.
Asunto(s)
Encéfalo/patología , Insecticidas/toxicidad , Neuroglía/patología , Neuronas/patología , Síndromes de Neurotoxicidad/etiología , Rotenona/toxicidad , Análisis de Varianza , Animales , Antígeno CD11b/metabolismo , Antígeno CD11c/metabolismo , Proteínas de Unión al Calcio/metabolismo , Caspasa 3/genética , Caspasa 3/metabolismo , Recuento de Células , Modelos Animales de Enfermedad , Relación Dosis-Respuesta a Droga , Regulación de la Expresión Génica/efectos de los fármacos , Proteína Ácida Fibrilar de la Glía/metabolismo , Masculino , Proteínas de Microfilamentos/metabolismo , Neuroglía/metabolismo , Neuronas/metabolismo , Síndromes de Neurotoxicidad/patología , ARN Mensajero/metabolismo , Ratas , Ratas Sprague-Dawley , Tirosina 3-Monooxigenasa/metabolismoRESUMEN
Rotenone induces neurotoxicity but its correlation with biochemical and cerebral changes in rat brain regions are not well defined. In the present study rotenone was administered (3, 6 and12mug/mul) intranigrally in adult male SD rats and its effect was assessed on neuromuscular coordination and in different brain areas viz. striatum (STR), mid-brain (MB), frontal cortex (FC) and hippocampus (HP) cerebral and biochemical changes on 1st and 7th day after treatment. All the doses of rotenone significantly impaired neuromuscular coordination performance on Rota rod test on 1st and 7th day. TTC staining showed significant increase in cerebral injury volume on 1st and 7th day after rotenone treatment indicating mitochondrial enzyme deficiency but increase after 7th day was less that after 1st day. Rotenone treated rats showed significant decrease in GSH and increase in MDA in different brain regions though the pattern was varied. After 1 day of rotenone (6 and 12mug) treatment significant decrease in GSH was observed in STR and MB while MDA was significantly increased only in MB. The maximal effect on GSH and MDA was obtained in STR and MB on 7th day after treatment with 12mug dose of rotenone. Thus, based on the occurrence of changes, it may be suggested that impairment of neuromuscular coordination is inked to oxidative stress rather than mitochondrial enzyme deficiency, all the processes are correlated with each other with the progression of time. MB appeared as most sensitive brain area towards rotenone toxicity.